Title: Resorbable Calcium Phosphate Ceramics for Bone Graft Abstract Calcium phosphate (CaP) based ceramics are used in hard tissue engineering because of their excellent biocompatibility. There is a need for the development of biodegradable ceramic materials with controlled degradation kinetics that will act as a scaffold and support bone remodeling. Our long range goal is to elucidate strength loss mechanism in CaP based material and scaffold to develop bone graft for specific application. Fundamental information on controlled degradation behavior of CaP based materials to identify optimal material composition can help us design and tailor resorbable tissue engineered bone replacement based on application needs. The objective of this research is to test our central hypothesis, which is chemistry and microstructure in CaP based ceramics can modify strength loss in these materials. Our preliminary data indicate that a minimum amount of trace elements (dopants) can have significant effects on physical and mechanical properties of CaPs. Cell-materials interactions can also be influenced by the presence of trace elements. The specific aims are 1) To investigate effects of nanoscale CaP with three different Ca to P ratios, 1.25:1, 1.33:1 and 1.5:1, through synthesis, processing, characterization and in vitro and in vivo bone cell-materials interactions. 2) To determine the effects of four dopants, Zinc, Magnesium, Silicon, and Strontium oxides in single and multi-element composition, along with three CaP ceramics with Ca:P = 1.25:1, 1.33:1 and 1.5:1 on in vitro and in vivo resorption. 3) To develop 3D interconnected tailored porosity CaP structures using rapid prototyping, with an average 300 microns pore size, and, 30 and 60 volume % porosity and verify the influence of porosity on their properties and study in vitro and in vivo interactions. In order to accomplish these aims, we will conduct a series of studies including synthesis of nanoscale CaPs with single and multi element dopants, characterize their chemical, physical and mechanical properties, and in vitro and in vivo strength loss behavior in rat and rabbit models. It is envisioned that results from the proposed study will lead to the development of CaPs with tailored degradation kinetics that can be used in spinal fusion, maxillo- and cranio-facial implants and small scale bone defect applications. Project Narrative Resorbable Calcium Phosphate Ceramics for Bone Graft Calcium phosphate (CaP) based ceramics are used in hard tissue engineering because of their excellent biocompatibility. The objective of this research is to test our central hypothesis, which is chemistry and microstructure in Calcium phosphate (CaP) based ceramics can modify strength loss in these materials. It is envisioned that results from the proposed study will lead to the development of CaPs with tailored degradation kinetics that can be used in spinal fusion, maxillo- and cranio-facial implants and small scale bone defect applications.